Wood, wood products, and wooden structures are vulnerable to degradation by wood-boring organisms. For example, wood boring-insects, such as termites, carpenter ants, and wood-boring bees (e.g. carpenter bees) cause considerable damage to buildings, fence posts, utility poles, and wooden supports.
Termites, particularly subterranean termites, are soil dwellers that exist in large colonies of several million termites. Members of the colony forage for cellulose-containing food items in the earth or above ground by building a system of closed mud tunnels to traverse from the ground to the above-ground food source. The ability of termites to cause considerable damage is in part due to the fact that they are not typically seen until termite infestation is at a relatively advanced stage, or that they cause damage to the interior of wooden structures or otherwise in places that are not readily observable.
Carpenter ants cause structural damage to wood, wood products, and wooden structures, such as homes, telephone poles, and trees by tunneling into the wood. Carpenter ants damage wood by hollowing it out for nesting, excavating galleries which have a smooth, sandpapered appearance. Wood that has been damaged by carpenter ants contains no mud-like material, as is the case with termites. Shredded fragments of wood, similar in appearance to coarse sawdust, are ejected from the galleries through preexisting cracks or slits made by the ants.
Wood-boring bees, such as carpenter bees, cause damage to wooden structures by boring into timbers and siding to prepare nests. Carpenter bee nests weaken structural wood and leave unsightly holes and stains on building surfaces.
Traditional methods for controlling wood-boring insects have included the application of insecticides and baiting systems. However, the effectiveness of such treatments has varied, and such treatment may introduce deleterious agents into the environment.
The use of wooden structures in the marine environment, such as piles or piers as structural supports for wharfs, bridges and other marine environment structures is well known. In particular, wooden pilings have been used for many years to support piers, wharfs, boat slips, and in some instances older bridges.
It is well known that such pilings are subject to many hazards necessitating repair or replacement. One major source of damage which drastically shortens the life expectancy of wood piling is attack by certain marine parasites and microorganisms which feed upon the cellulose material of the wood piling.
Particular marine microorganisms known to attack wooden pilings include limnoria and teredo microorganisms. The teredo, also known as shipworm, are marine, bivalve mollusks, typically on the order of 10 inches in length or less, although they have been known to grow to as much as 2 feet or more in length and have diameters of half an inch. The shipworm begins life as a larva and begins its metamorphosis into an adult when it has attached itself to the surface of a piece of submerged timber.
It is believed that the shipworm begins burrowing into the submerged timber and its tail appendage seals off the entry way. The shell valves of shipworms take the form of two small anterior members with file-like ribs, which are specialized for boring. By means of alternating contractions of the muscles that actuate the valves, the file-like ribs produce a cutting action that enable shipworms to bore into the wood they infest. Thereafter, they consume the structure by digesting the cellulose of the wooden members. In its boring, a shipworm will dispose of waste through an exhalation syphon and an inhalation syphon is designed to produce continuously circulating water over the shipworm's gills for the absorption of oxygen. New larvae are also disposed of through the exhalation syphon to infest the same submerged timber or other timber.
Typically, the only visible presence of a shipworm is the occurrence of two microscopic syphon tubes, one for the inhalation of fresh water and the other for exhalation. The specific danger with the shipworm is that the submerged timber pile appears to be secure and intact, when in fact, the interior of the pile may contain a great deal of infestation, thus weakening the pile.
A second marine borer, of the limnoria species, also referred to as a gribble, resembles lice and is about 5 mm (0.2 in) long. Gribbles live on submerged wood; for example, piers, bridge piles, and ship hulls and are capable of boring holes of approximately 3 mm in diameter. Gribbles destroy the structures they infest by burrowing at close intervals into the members that make up the structure and consuming the wood from which they are made.
Limnoria rarely penetrate the timber for more than 10 to 12 millimeters, but they normally infest in great numbers on the outer layer of the submerged timber such that the submerged timber takes on a honeycombed appearance with tiny individual channels. This attack, combined with the eroding effects of the sea's tide, breaks down the surface of the wood and exposes new surfaces for attack.
Previous efforts to safeguard wood-containing structures from marine microorganisms have included impregnating the structures and/or coating their surfaces with materials such as creosote. The use of poisonous, chemical agents, however, is of limited effectiveness and has associated negative side effects. For example, many jurisdictions have effectively banned the use of creosote in coastal waters.
As a second approach to avoiding the effects of mariner borer attack, workers seeking to control them have found they can be killed by suffocation. Specifically, biologists have noted that gribbles and shipworms rely on contact with sea water to get the oxygen they require for survival. Accordingly, marine engineers have proposed ways for interrupting the supply of sea water to the structural members borers infest. However, the effectiveness of such measures has varied.
Thus, there is a continuing need for an improved approach for protecting wood, wood products, and wooden structures from borer infestation, particularly in a way that is environmentally friendly.